Antifogging agents are commonly used in transparent packaging materials or films (Plastics Additives Handbook, 5th Edition, 2001, Hanser Verlag, pp. 609-626). Antifogging agents produce transparent layers on the packaging films by preventing the formation of water droplets on the plastic surface in the event of the condensation of water. Plastics generally have a high interfacial tension towards water and are therefore water-repellent, so that water in the form of droplets rather than a uniform film is deposited on the surfaces. In the absence of antifogging agents, the “fog” is formed on the inside of the goods wrapped in packaging films, so that the contents of the package are no longer visible. In addition, droplets of condensed water are a favorable medium for the proliferation of food-damaging germs and microorganisms.
Accordingly, it is desirable to reduce the surface tension of the plastics towards water which is done by hydrophilicizing the plastics. So-called “internal” and “external” antifogging agents are suitable for this purpose. Internal antifogging agents are directly added to the plastic while external antifogging agents are applied as a coating to the plastic surface. Although external antifogging agents are instantly effective, they are not long-lasting because they can simply be washed off or removed. Accordingly, a long-term effect can only be achieved with internal antifogging agents which are incorporated in the polymer matrix of the plastic and diffuse slowly to the surface of the substrate. Internal antifogging agents have to meet stringent compatibility requirements in particular in the food industry. Besides being compatible with foods, they have to be suitable for the processing of the plastics, i.e. heat-stable at the corresponding processing process temperatures. They must not adversely affect the transparency of the films or the printing and sealing properties of the films or lead to discolouration or odor emissions. In addition, ecologically safe, but economically favorable processes are becoming increasingly important in particular in the plastics-processing industry.
Accordingly, the problem addressed by the present invention was to provide an antifogging agent which would satisfy the various requirements mentioned above without having any of the disadvantages referred to.